docs(handover): merge AI-WORK-007-UPSTREAMS.md into AI-WORK-007.md §A

Per user instruction, collapse the two 007 working docs into one
with split sections. The former UPSTREAMS.md is appended as §A
"Upstream Dependency Chains" — per-open-item walk from highest-level
upstream (external / human gate) down to the 007-lang file,
ordered by action-cost.

- docs/handover/AI-WORK-007.md — now 1139 lines (§0..§6 unchanged,
  new §A at end).
- docs/handover/AI-WORK-007-UPSTREAMS.md — removed (content merged).
- docs/handover/README.md — index updated.

No general-work items were split out — AI-WORK-007 was self-contained
(the GitHub billing L0 blocker referenced in §A §1 is already tracked
in ~/Desktop/YOUR-ACTIONS-todo.md §1).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath